Sartar is usually described as a pretty rural place, with a relatively small urban population; Sartar: King of Heroes, for example, claims less than 10% of its populace live in cities. But the numbers seen in the Guide to Glorantha don't seem to line up with that portrayal, and certainly not with that proportion. Those numbers are 25,000 urban and 100,000 rural, which would mean that a full 20% of Sartar's population are living in cities, a much greater proportion than many places that are described as being very urban.
Now, part of this is because it's counting the 5,000 people living where they work at the New Lunar Temple, but even if we throw that one out, that's still 20,000 and 100,000, meaning 1/6th of Sartar's populace is urban, and that's still a lot for a supposedly rural "barbarian" kingdom, and that in turn raises the question of how you could support that many. And most of that is down to Boldhome having a population of 11,000.
So, is the answer that Boldhome is just dangerously, unsustainably overpopulated? Has its population swelled by thousands over the course of the Lunar Occupation, for example? How are they keeping that many people fed, when the city is built into a mountain and there's really only so much you could possibly buy or take as tribute/taxes from the surrounding tribes?